Subtractive color photography



Sept. 12,1933,

TRANSMISSION J. A. BALL 'susrmcnvn COLOR PHOTOGRAPHY Filed March 3, 1931NEGATIVES MATRICES 2}, El

, 7 -;2. {g POSITIVE jzu7c707 Jse B Patented Sept. 12, 1933 UNITEDSTATES SUBTRACTIVE COLOR PHOTOGRAPHY Joseph A. Ball, Los Angeles,Calif., assignor, by mesne assignments, to Technicolor, Inc., New York,N. Y., a corporation of Delaware Application March 3, 1931. Serial No.519,721

2 Claims.

It is known to combine subtractive three-color reproductions with blackor gray key prints in order to improve the definition of the final printand to obtain actually black portions without the necessity ofespecially balancing and controlling the color aspects for this purpose.It has also been proposed to use one of the color separation negativesor a combination thereof for making the key print instead of making aspecial exposure for this purpose. -The present invention is animprovement of these known methods and some of its objects are toutilize the known advantages of the key print and at the same time tobalance the color aspect prints by means of the key print. to utilizeoverlapping taking filters without unbalancing any color in the finalprint, to make well balanced threecolor positives with key prints fromthree-color separation negatives, to make colored cinematographic filmswith silver sound track and key print for the pictures in a simplecomparatively inexpensive and commercially feasible manner, and toeliminate unbalance of the middle range of the spectral colors in colorseparation reproductions. Other objects will be apparent from thefollowing description and the accompanying drawing in which:

Fig. 1 is a diagram showing the transmission curves of filters for colorseparation photography;

Fig. 2 is a schematical illustration of an embodiment of the presentinvention.

In the course of experimentation with threecolor photography I havefound that in the final positive the colors of the middle range of thespectrum are not rendered as correctly as those of the marginal ranges.This is probably due to imperfect color separation in this range causedby'the double overlap of the taking filters in 40 this range since, aswell known in the art, it is not possible to obtain sharply cutfiltering means, and in order to obtain the maximum light intensitywhich is very necessary in color separation photography a certainoverlap of the filters as shown in Fig. 1 must be tolerated.Consequently the middle range of the spectrum is finally rendered notonly with the printing colors corresponding to the ideal colorseparation but also with other colors actually not belonging there,which results in a general graying down or lowering in key of thisrange. corresponding to the superimposition of colors adding up toblack.

It is well known in the art that a subtractively produced color printcan be much improved by adding a so-called key print, which supplies ina convenient manner the desirable definition otherwise afforded bythree-color processes only with many difliculties and therefore only ata much greater expense. With a key print in the form of an imageassuring the best obtainable sharpness, as for example a silver image,the color aspects need only be perfect as far as color rendition isconcerned and it is not necessary to perfect them with a view toobtaining maximum definition and correctrendering of the blacks. This isthe more important as these two requirements, namely correct colorrendition and correct rendering of the blacks together with gooddefinition, are in many cases exclusive of each other or at least verydiflicult to reconcile.

I have found that the introduction of a key print according to thisinvention'also corrects the imperfect rendering of the middle rangereferred to above. Using the terms commonly employed for the dominatinghues of the corresponding spectral ranges, the taking ranges for thenegatives are separated with the aid of blue, green and red takingfilters and the subtractive positives obtained from these negatives areprinted with the complementary colors, yellow, magenta and cyanrespectively. A black and white key print corresponding to the overallcolor intensities of the scene, as for example one taken through ayellow filter on a panchromatic emulsion, darkens the various partialprints of the positive to an equal degree; and with such a key print themiddle range will be lower in key just as in a pure three-color print.Now according to the present invention I use the negative obtainedthrough the green filter for making the key print positive. Since anobject having colors predominantly of the middle range of the spectrum(herein called a green object) is reproduced with the cyan and yellow 95of the positive, the reproduction of such an object is not furtherdarkened by the key print produced from the green negative, which isalso printed in magenta, whereas the positive reds and blues arecontrolled by the magenta print made from the green negative and, sincethis magenta print coincides in its density distribution with the keyprint, the positive reds and blues become lower in key and are in thismanner brought into better balance with the greens.

Having now described my invention in a general manner I shall proceed togive a more detailed description of one of the possible concreteembodiments thereof with reference to Fig. 2 of the drawing.

With an appropriate arrangement (such as for example described in detailand claimed in my co-pending application Serial No. 460,161, filed June14, 1930) consisting of a light splitting optical system which permitsthe exposure of three films, through suitable filters, I take threecolor separation negatives B, G, R, on films 1, 2, 3, with taking rangesaccording to Fig. 1. As indicated in Fig. 2, from the negative G I makea positive print K in the ordinary silver bromide emulsion of a film 6,preferably under-exposing this print since the beneficial function ofthe key print is mainly in the higher densities. A gamma ofapproximately unity is to be preferred for the key print which makes itpossible to print it together with a photographic sound track positive7, sound tracks requring such a gamma. This has the additional advantageof utilizing a necessary step in the manufacture of sound films for thepicture film, thereby eliminating any extra cost for the key print ofthe improved picture record. From the color separation negatives Iproduce printing matrices 10, 11 and 12, with positive images Y, M andC, preferably according to methods disclosed in various patents to theTechnicolor Motion Picture Corporation. From these matrices I print byimbibition, transferring dyes from the matrices in consecutive steps tothe gelatine emulsion already containing the key print and, if desired,the sound track. It is of course understood that it may be preferable incertain cases to print the sound track from one or several matricestogether with the color aspects as disclosed in the co-pendingapplication of L. T. Troland, Serial No. 327,420, filed December 20,1928 and assigned to the same assignee. In this manner I obtain a finalpositive P containing a key print and three color components which arebalanced by the key print and also having all the well known desirablefeatures of a three-color positive with key print.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim:

1. The method of making color photographs which comprises making threecolor separation negatives of difierent spectral ranges of a scene,making a black and white positive key print from the color negative ofthe intermediate spectral range and superimposing the on positives ofthe color separation negatives 'in colors complementary to therespective taking ranges.

2. The method of making color photographs which comprises taking colorseparation negatives of the overlapping red green and blue spectralranges of a scene, photographically printing from the green negative, ina silver halide emulsion, an under-exposed key print, developing it to agamma of approximately unity and superimposing thereon by imbibitionpositive prints of said color separation negatives in cyan, magenta andyellow.

JOSEPH A. BALL.

